Hi, I'm Harold
Fullstack Engineer (Backend-focused)

Fullstack Engineer (Backend-focused) · HCMC, VN

• Advertising Platform. Building an advertising platform for advertisers and publishers on a lean team (4 BE, 2 FE). Own the authorization and bidding services and ship across the stack, from requirements to deployment and data migration.
• Ad Serving & Bidding. Built the ad-serving and bidding engine for CPC and CPD campaigns with a linear-regression bid model. Handled about 5 billion ad requests in the first 3 months.
• Authorization (OpenFGA). Designed the permission model: partner-scoped access for advertisers down to near row-level checks, using OpenFGA + RBAC.
• Reporting Performance. Cut reporting latency with multi-layer Redis caching, materialized views and historical backfill on PostgreSQL/Aurora, ClickHouse, BigQuery and Airflow.

Fullstack Engineer · HCMC, VN

• Notification Service. Managed backend on an 8-person team for a 10M MAU app. Owned push and in-app newsfeed on Kafka fan-in/fan-out with batching, dedup, idempotent delivery and retry/DLQ so spikes of 1-2M users did not pile up.
• Internal RAG Assistant. Built a RAG assistant over Jira, Slack and internal Wiki with Qdrant, LangChain/LangGraph and FastAPI, run locally to keep data in-house. Saved roughly 10h/person/week on cross-tool search.
• Naver AI Hackathon 2025. Won 3rd place at Naver's internal AI Hackathon 2025 and presented AI agents and agentic workflows to the whole company.
• Airflow Crawlers. Replaced manual data entry with an Airflow crawling platform: 200+ DAGs across ~20 sources, ~600 pages per run, publishing to Kafka for ETL.
• Schema, Deploy & Cost. Owned schema design for 200GB+ databases and zero-downtime schema changes across ~10 services on Kubernetes/ArgoCD. Cut AWS data-transfer cost by moving internal traffic to VPC endpoints.

Fullstack Web Engineer · HCMC, VN

• Warehouse Safety Product. Fullstack on a 5-person team: NestJS microservices and admin/customer/monitoring UIs in React + Ant Design.
• Redshift Warehouse & Alerts. Built a 100GB+ Redshift warehouse with AWS Glue ETL over labeled warehouse-worker video, used for risk reports and real-time accident alerts.

Associate Software Engineer · HCMC, VN

• Wikidata Pipeline. Built data-collection and backend services in Java/Python (Vert.x, GraphQL) to replicate and process 200GB+ Wikidata for rule-based and ML QA.